Modern supratidal microbialites fed by groundwater: functional drivers, value and trajectories
- Authors: Rishworth, Gavin M , Dodd, Carla , Perissinotto, Renzo , Bornman, Thomas G , Adams, Janine B , Anderson, Callum R , Cawthra, Hayley C , Dorrington, Hayley C , du Toit, Hendrik , Edworthy, Carla , Gibb, Ross-Lynne A , Human, Lucienne R D , Isemonger, Eric W , Lemley, David A , Miranda, Nelson A , Peer, Nasreen , Raw, Jacqueline L , Smith, Alan M , Steyn, Paul-Pierre , Strydom, Nadine A , Teske, Peter R , Welman, Peter R
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/426008 , vital:72306 , xlink:href="https://doi.org/10.1016/j.earscirev.2020.103364"
- Description: Microbial mats were the dominant habitat type in shallow marine environments between the Palaeoarchean and Phanerozoic. Many of these (termed ‘microbialites’) calcified as they grew but such lithified mats are rare along modern coasts for reasons such as unsuitable water chemistry, destructive metazoan influences and competition with other reef-builders such as corals or macroalgae. Nonetheless, extant microbialites occur in unique coastal ecosystems such as the Exuma Cays, Bahamas or Lake Clifton and Hamelin Pool, Australia, where limitations such as calcium carbonate availability or destructive bioturbation are diminished. Along the coast of South Africa, extensive distributions of living microbialites (including layered stromatolites) have been discovered and described since the early 2000s. Unlike the Bahamian and Australian ecosystems, the South African microbialites form exclusively in the supratidal coastal zone at the convergence of emergent groundwater seepage. Similar systems were documented subsequently in southwestern Australia, Northern Ireland and the Scottish Hebrides, as recently as 2018, revealing that supratidal microbialites have a global distribution. This review uses the best-studied formations to contextualise formative drivers and processes of these supratidal ecosystems and highlight their geological, ecological and societal relevance.
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- Date Issued: 2020
Diversity and ecological role of true crabs (crustacea, brachyura) in the St Lucia Estuary, iSimangaliso Wetland Park, in response to global change
- Authors: Peer, Nasreen
- Date: 2016
- Subjects: Crustacea -- South Africa -- KwaZulu-Natal Crustacea -- South Africa -- Saint Lucia, Lake , Global environmental change
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/45558 , vital:38669
- Description: This work has explored novel concepts of crab vulnerability, recovery and resilience under unprecedented climatic changes in South Africa’s first UNESCO World Heritage Site. By showing how large salinity shifts and prolonged interruption of the marine connection can drastically affect brachyuran diversity and community structure in St. Lucia Lake, the potential cascading effects on ecosystem functioning were estimated. Only 15 crab species were recorded within the system during this study, compared to the 26 species that were known to occur prior to the recent environmental shift (i.e. 58% decline). The impact of this biodiversity collapse has negatively affected the associated mangrove ecosystem in particular, with the entire community of fiddler crabs persisting only in a small area near the estuary mouth. Gut fluorescence measurements have shown that, due to a lack of tidal Influence, their grazing impact on microphytobenthic biomass may become unsustainable. However, although adults are able to survive in this environment, the larvae require a marine connection; and they are thus unable to tolerate the wide fluctuations in salinity currently prevailing in the system. The study concludes that brachyurans are key factors to consider during conservation planning, as they are crucial to maintaining ecosystem function in the face of environmental change. This research is of global relevance, as many similar estuarine and coastal lakes around the world are currently experiencing similar state shifts. All six chapters included in the thesis have already been published in the peer-reviewed literature; and the project results have also earned Nasreen the NRF award of Next-Generation Researcher of the Year for 2015.
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- Date Issued: 2016
Tufa stromatolite ecosystems on the South African south coast
- Authors: Perissinotto, Renzo , Bornman, Tommy G , Steyn, Paul-Pierre , Miranda, Nelson A F , Dorrington, Rosemary A , Matcher, Gwynneth F , Strydom, Nadine A , Peer, Nasreen
- Date: 2014
- Language: English
- Type: Article
- Identifier: vital:6490 , http://hdl.handle.net/10962/d1014585 , http://dx.doi.org/10.1590/sajs.2014/20140011
- Description: Following the first description of living marine stromatolites along the South African east coast, new investigations along the south coast have revealed the occurrence of extensive fields of actively calcifying stromatolites. These stromatolites have been recorded at regular distances along a 200-km stretch of coastline, from Cape Recife in the east to the Storms River mouth in the west, with the highest density found between Schoenmakerskop and the Maitland River mouth. All active stromatolites are associated with freshwater seepage streams flowing from the dune cordon, which form rimstone dams and other accretions capable of retaining water in the supratidal platform. Resulting pools can reach a maximum depth of about 1 m and constitute a unique ecosystem in which freshwater and marine organisms alternate their dominance in response to vertical mixing and the balance between freshwater versus marine inflow. Although the factors controlling stromatolite growth are yet to be determined, nitrogen appears to be supplied mainly via the dune seeps. The epibenthic algal community within stromatolite pools is generally co-dominated by cyanobacteria and chlorophytes, with minimal diatom contribution.
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- Date Issued: 2014